Saturn INT-20
| Function | Manned LEO launch vehicle | 
|---|---|
| Manufacturer | Boeing (S-IC) Douglas (S-IVB) | 
| Country of origin | United States | 
| Size | |
| Height | 85 m (279 ft) | 
| Diameter | 10 m (33 ft) | 
| Mass | 2,304,000 kg (5,079,000 lb) | 
| Stages | 2 | 
| Capacity | |
| Payload to LEO | |
| Mass | 60,500 kg (133,400 lb) | 
| Launch history | |
| Status | Proposal | 
| Launch sites | LC-39, Kennedy Space Center | 
| First stage - S-IC | |
| Engines | 3-5 Rocketdyne F-1 | 
| Thrust | 34.02 MN (7,650,000 lbf) | 
| Burn time | 212 seconds | 
| Propellant | RP-1 / LOX | 
| Second stage S-IVB | |
| Engines | 1 Rocketdyne J-2 | 
| Thrust | 1 MN (220,000 lbf) | 
| Burn time | ~475 seconds | 
| Propellant | LH2 / LOX | 
The Saturn INT-20 was a proposed intermediate-payload follow-on from the Apollo Saturn V launch vehicle. A conical-form interstage would be fitted on top of the S-IC stage to support the S-IVB stage, so it could be considered either a retrofitted Saturn IB with a more powerful first stage, or a stubby, cut-down Saturn V without the S-II second stage.
Three variants were studied, one with three F-1 engines in the first stage, one with four, and one with five.